Logres - Quondam et Futurus

It's not quite proof . . . but it is an indication that there may be more to the King Arthur stories than historians would  have you believe.

Geoffrey of Monmouth seems to have been the first to write about King Arthur.  Alas, a good many members of academe even at the time didn't take it seriously.  Geraldus Cambrensis didn't actually refer to our author as  "Lyin' Geoffrey" but  he did opine that it was well-known that placing the New Testament upon the chest of a possessed person would drive the devil out.  However, if you placed a copy of Geoffrey's book on the person's chest a hundred more devils would show up.

In any event, Geoffrey said that King Arthur was born at Tintagel peninsula in Cornwall.  "Tosh", said Geraldus and good many others ever since.  But now it seems that the remains of something akin to a royal palace have been found at Tintagel dating from around the time of, oh, say, King Arthur.

You can read about it here.